Chromium/silica-titania catalysts can be used to make HDPE. The addition of titanium to chromium/silica can increase the activity of the catalyst, but more importantly, can increase the melt index potential of the catalyst, i.e., the ability of the catalyst to produce higher melt index or higher melt flow polymers. Often, titanium addition has been accomplished via an anhydrous route, using titanium alkoxides impregnated onto chromium/silica from a suitable organic solvent, such as a hydrocarbon, an alcohol, or an ether. This anhydrous route requires subjecting the silica to a prolonged drying step at elevated temperatures to remove adsorbed moisture, which could react with the titanium alkoxide and prevent it from attaching to the silica. Further, after titanium deposition, another prolonged drying step is needed to remove organics from the solvent and the alkoxide (e.g., resulting in VOC emissions). Melt index potential also can be lost during this drying step. For at least these reasons, the anhydrous process is performed batchwise, which can further increase cost and reduce efficiency.
In view of these drawbacks, it would be beneficial to provide improved methods for making titanated chromium catalysts. It is to this end that the present invention is generally directed.